Negative transconductance device and circuit



March 5, 1946. M G CROSBY 2,396,088

NEGATIVE TRANSCONDUCTANGE DEVICE AND CIRCUIT Filed Nov. 26, 1941 6 I ourpur OUTPUT INVENTOR MURRAY GCROSBY BY .ATTORNEY tune out the screen to ground capacity. The circuit Z is tuned to the frequency of the input waves and comprises a condenser and an inductance in electrically parallel relation. The tuned circuit Z is-thus a substantially pure resistance at the operating frequency because it is antiresonan-t, and in this way I am able to obtain the necessary IR drop in the screen circuit, in response to a rise or fall in potential on the control grid. Th circuit will also function by shunting the resistor R with the tuned circuit Z, in which case the tuned circuit would be damped by resistor R.

Fig. 3 illustrates how the. -principles of the present invention can be applied to an oscillation generator. In Fig. 3, the parallel tuned circuit L, C is the output circuit. A feed back condenser C1 is connected between the output tuned circuit and the first or control grid G1 for feeding back energy from the plate which is in phase with the voltage on "the control grid. The resistor R1 is'the grid return resistor. with the circuit as shown in this figure, oscillations will be maintained as long the frequency is not high enough to enable the screen to ground capacity of the vacuum tube to bypass the screen resistor R. Here again, if it is desired to employ the oscillation generator at high frequencies, I may tune out the screen to ground capacity by replacing the resistor R with a tuned circuit Z, in themannershown in Fig. 2.

The oscillator of Fig. '3 can-be converted into a multivibra'tor circuit by replacing the tuned circuit L, C with a resistance. If this resistance is made small compared to theconstants of R1 and C1, then "the grid return resistor R1 and condenser C1 will determine the frequency oi. the relaxation oscillations.

Fig. 4 illustrates a'modiiication of Fig. 1, where- .in the multi-grid vacuu'm'tube TI is replaced by a four-electrode screen grid tube I". The operation of "the circuit of Fig. 4 will be apparent from the descriptiongiven above for Fig. '1.

I have found that a practical negative resistance device in accordance with the invention may comprise an RCA 6-L-'7 tube with 170,000 ohms in the screen circuit "for resistor R and 800 ohms for "the cathode circuit 101- the resistor '12 With such a circuit, bypassing of the cathode resistor seems to have very little effect onthe operation of the circuit.

Although the invention has'be'en described with particular reference to a pentagrid vacuum tube,

it should be understood that the invention is not limited to the use of such a tube, since, if desired, a screen grid or iour-elec'trode'tub'e can 'be employed in accordance with my teachings without departing from the spirit and scope of the invention.

"What is claimed is:

1. An electron discharge device oscillation gen erator system obtaining negative 'transconduc- 'tance between input and output electrodes, comprising an evacuated envelope having therein a cathode, a control electrode asan'input electrode, a screen electrode, and an output electrode, a connection from said screen electrode to 'thepositive terminal of a source of unidirectional potential, 2. parallel tuned circuit tuned to the operating fre- 'qu'ency of said generator connected between the output electrode andsa'id "positive terminal of said source of unidirectional potential, "an "impedance circuit substantially resistive at the operating frequency in said ccnnection'between the screen electrode and said source of unidirectional potential,

said impedance circuit having suiliciently high valueto produce the negative transconductance efiect, a feed-back circuit consisting of a condenser connected between said output electrode and said input electrode for feeding back energy from said output electrode which is in phase with the voltage on the input electrode, and a resistor connected between said input electrode and said cathode.

2. A negative resistance adapted to produce oscillations when connected across a resonant circuit of relatively low frequency, comprising a vacuum tube having in the order named, a cathode, a control electrode, a grid, a. screenand an output electrode, a resistor connecting said cathode to groundm connection from said output electrode to one terminal of resonant circuit, a capacitive connection from the grounded end of said resistor to theot'her terminal of said resonant circuit, an unbypassed resistor connected between said screen and said last terminal of said resonant circuit, and a connection from said last terminal to the positive terminal of a source of unidirectional potential, said unbypassed resistor being or a value suilic'iently high to produce the negative transconductance effect, a direct connection between said grid and ground, a resistor between said control electrode and the grounded and of said first resistor, and a feed back circuitbetween said output and control electrodes for capacitively feeding back energy from the output "electrode which is in phase with the voltage on the control electrode, said feed back circuit beingdevoid of inductance coupling e'ifects.

3. An electron discharge device oscillator system utilizing the negative 'transcon'ductance phenomena, said device having a cathode. an input electrode, a screen electrode, and an output electrode; a connection having substantially purely resistive impedance of a su'mciently high resistance to produce the negative transconductance effect at the operating frequency between said screen electrode and the positive terminal of a source of unidirectional potential, 9. feed back circuit devoid of inductive coupling andcomprising a condenser coupled between said output and input 'e1ectrodes,and a 'tunsd'outputcircuit tuned to the operating frequency ofsa'id oscillator system coupled between said output elec'trodeand cathode, a resistor connected between said input electrode and said cathode, whereby'a rising positive potential on said input electrode causes a decrease in the electron current to said output electrode.

4. An electron discharge device oscillator system obtaining negative transconductanc between input and output electrodes, comprising a pentagrid tube having .a firstgrid asan input electrode and an anode as an output electrode, a direct connection between the the second and fourth grids to constitute a screen for the third grid, adirect connection between the .flith grid and the cathode, a direct connection between the third grid and ground, a connection having substantially purely resistiv impedance of 1a suiliciently high value to produce the negativetransconductance efiect at the operating frequency extending 'from the screen to the positive terminalof a source of unidirectional potential whose negative terminal is connected to :ground, a resistor of relatively small value connected between said cathode and ground, a parallel tuned output ci-rmiit connected between said output electrode and the posltiveterminal of a source of polariiing potential, a capacity feed connected between said "output and input electrodes. and a resistor connected between said input electrode and ground. I V

5. An electron discharge device oscillator system obtaining negative transconductance, comprising a vacuum tube having therein a cathode, a first grid, a second grid, ascreen grid, and an anode, a direct connection between said second r grid and ground, a connection including a resistance of relatively high value extending from said screen grid to the positive terminal of a source of 10 imidirectional potential whose negative terminal is connected to ground, a resistor of relatively low value connected between said cathode and ground, a parallel timed output circuit connected between said anode and the positive terminal of a source of polarizing-potential, a capacityieed-back circuit devoid of inductive coupling effects connected between said anode and first grid, and a resistor connected between said first grid and ground.

MURRAY G. CROSBY. 

